Method of splicing polyamide yarn and bonding composition therefor



United States Patent 3,386,871 METHOD OF SPLICING POLYAMIDE YARN ANDBONDING COMPOSITION THEREFOR Grady N. Dulin, J12, and John I. Scott,Chester, Va., as-

signors to Allied Chemical Corporation, New York,

N.Y., a corporation of New York No Drawing. Filed May 10, 1963, Ser. No.279,615

5 Claims. (Cl. 156-158) ABSTRACT OF THE DISCLOSURE The inventionprovides a bonding composition useful for uniting multifilamentpolyamide yarns, wherein a polyamide of formic acid relative viscosityat least about 50 is dissolved at 8%-17% concentration in a solvent ofboiling point between 90 C. and 115 C. to form a solution of viscosityat room temperature between 2500 and 6000 cps. Such composition can beapplied with no more than slight warming whereby it can be applied byhand. It forms a permanent bond in a few seconds which sets 1n a fewhours to a strength such as 70% of the breaking strength of the yarn andwhich is flexible allowing a textured effect at the bond and withstandselevated temperatures and moisture.

This inventionrelates to the uniting of ends of multifilament polyamideyarns with bonding compositron s, to novel bonding compositions usefultherefor contalning dissolved polyamide, and to uniform yarns therebyobtained made up of smaller yarn segments cohesively united by saidbonding compositions.

In the utilization of continuous multifilament yarns in various textileapplications, specialized packages of yarn are generally employed inaccommodating the various specific requirements of textile processes andmachinery. During the formation of specialized yarn packagesdiscontinuities due to yarn breakage or the run-out of feed sources mayoccur prior to completion of the pack age. In yarn packages such asconvolutely wound cones, beams, tubes, pirns, spools, bobbins, and thelike designed for use in texturizing, weaving, knitting, t-ufting, orother textile operations, the uniting of ends by knotting is generallyfound unsatisfactory. The presence of such knots in the yarn causesdifficu-lties in subsequent textile operations; and, when present in thefinished textile article, detracts from the desired aesthetic qualitiesof the product.

In utilizing continuous multifilament synthetic yarns in the productionof textile articles, it is frequently necessary to increase the bulk orcovering power of the yarn to a degree approximating that of spun cottonand woolen yarns. The bulking or texturizing processes are generallyaccomplished by methods such as crimping, heat curling, and analogoustechniques wherein the yarn is generally subjected to physical forcescapable of deforming the individual filaments under conditions ofelevated temperature, and usually in the presence of steam or otherplasticizing agents. For example, in stufiier-box crimping operationscarried out on multifilament polycaprolactam yarn, the crimp settingconditions quite frequently employed require steam at temperaturesbetween about 120 and 140 C., for periods up to 10 seconds acting on thehighly compressed yarn structure. In such stuffer-box crimpingoperations, the presence of knots is found undesirable in view of thenonmniformities and entanglements they produce. Although it is knownthat yarn ends can be spliced or united without knotting by applicationof adhesives, it is generally found that an adhesive bond is easilyweakened or broken under the hot, wet conditions generally experiencedby yarns during texturing operations or during subsequent hot stretchingoperations. In order to se cure adequate dry strengths with adhesiveagents it has generally been found necessary to extend the length of thespliced section to over /2 inch; and such spliced sections are generallyfound too stiff or bulky to be textured, and will not pass through thefine guides and needles utilized in textile manufacturing operations. 7

Suitable splicing methods, to be satisfactory in operation must becapable of rapid execution with minimum disruption of the continuousoperations of the synthetic fiber manufacturing operation. An acceptablebonding composition must therefore be capable of quickly effecting anacceptable strength splice in a non-tacky condition without materiallyaltering the over-all yarn path.

It is an object of this invention to provide a method for rapidlyforming a strong splice between ends of a continuous multifilamentpolyamide yarn. It is another object of this invention to providebonding compositions capable of rapidly effecting a strong non-tackyshort splice between two ends of a multifilament polyamide yarn, saidspliced portion being crimpable. It is a still further object of thisinvention to provide a method of making uniform knotless texturedmultifilament polyamide yarn consisting of two or more segments unitedby a short splice resistant to breaking under hot, wet crimpingconditions. Other objects and advantages will become apparenthereinafter.

The objects of this invention are accomplished in general by applying toportions of polyamide multifilament yarns a practically saturatedsolution of 8%-l7% of a polyamide of formic acid relative viscosity inthe high range, suitably the ultrahigh range, at least about 50 anddesirably l00250. 'Formic acid relative viscosity, hereinafterdesignated V. Rel., is determined in aqueous formic acid solution of 11grams of polymer per ml. of solvent, at 25 C., by ASTM method No.D-789-53T, using polymer which has been leached with hot water to removethe low molecular weight constituents. The solvent used must have aboiling point between 90 C. and C., and the solution must have viscosityat room temperature between 2500 and 6000 centipoises. The impregnatedfilaments to be bonded are brought into intimate contact over a lengthsuitably about A inch-V2 inch, and the solvent is then allowed toevaporate.

Typically the polyamide composing the filaments bonded in this inventionwill have V. Rel. in the range from about 30 to about 80. Dissolvedpolyamide materials useful in the practice of this invention arecharacterized by recurring carbonamide groups in the backbone chain ofthe polymer, and include polymers of lactams such as caprolactam andlactams of smaller or larger ring size; polymers of diacid-diaminecombinations such as poly(hexamethylene adipamide) and aromatic analogsthereof; and polyamide compounds which have been submitted to chemicalmodification, such as methoxymethylated polyamides. In order to secureadequate strength, flexibility, and bonding characteristics, thepolyamide should have, as above stated, V. Rel. of at least about 50.Higher viscosity materials, up to V. Rel. of 350 and greater, can beused as long as the concentration remains in the specified 8%17% rangeand the solution viscosity remains in the 25006000 poise range. The V.Rel. can be correlated with polymer number average molecular Weights. V.Rel. of 50 corresponds approximately to number average molecular weightof 15,000; V. Rel. of 65 corresponds approximately to number averagemolecular weight of 20,000; V. Rel. of 100 corresponds approximately tonumber average molecular weight of 25,000; and V. Rel. of 350corresponds approximately to number average molecular weight of 40,000.

The solvents useful in the practice of this invention must have anafiinity for the yarn such that the solvent is capable Patented June 4,1968 of dissolving the yarn at room temperature. It has been found thatthe volatility of the solvent should be such that its boiling point isbetween about 90 C. and 115 C. Solvents having a lower boiling pointgenerally lead to difiiculties in the application of the bondingcomposition to the yarn, and yield inferior quality splices. Solventshaving a boiling point above 115 C. evaporate too slowly to yield anon-tacky splice in reasonably short time. The solvent should be capableof forming saturated solutions of the dissolved or bonding polyamidecontaining between 8% and 17% of the dissolved polymer at roomtemperatures, and solutions having viscosities between about 2500 and6000 centipoises. Viscosity values outside of the herein-prescribedrange lead to splices of inadequate quality. It is generally preferredto employ solvents which are relatively non-toxic, non-inflammable andnon-corrosive. Mixtures of pure solvents may be employed to secure acomposite solvent having the characteristics required in the practice ofthis invention, in which case minor amounts of solvents having a boilingpoint within about 25 C. outside the preferred range may be employed,and especially solvent mixtures which form azeotropic combinations.Preferred solvents useful singly or in combinations include:tetrafiuoropropanol, chlorodifiuoroethanol, and other species analogousthereto, e.g., trifiuoroethanol.

The bonding composition may be applied to the yarn ends by hand, astaught in U.S. Patent 1,986,974, or may be applied mechanically by meansof rollers, extruders, troughs, belts, or analogous devices. Similarly,the yarn ends containing the viscous solution of polymer may be broughtinto intimate contact by hand or mechanical devices, and supportedmechanically or by hand under no tension until the solvent has partiallyevaporated. Solvent evaporation may be effected at room or elevatedtemperatures under static air conditions or by contact with a stream ofair. The overlapped portion of the two yarn ends which constitute thesplice should be not over /2 inch in length.

Yarns containing splices prepared in accordance with this invention canbe subjected, without breaking, to crimping operations employing astuffer-box as described in U.S. Patents 3,037,260 and 3,031,734. Foreffective crimping and setting of a polyamide yarn by stuifer-boxmethods, temperatures in the range of about 110 C. to 140 C. areemployed, generally in the presence of moisture which facilitates thecrimping and setting operations. Under such conditions, ordinaryadhesive-based splices are unreliable, exhibiting failure probabilitiesin excess of about 1%. It has been found that the reliability of splicesunder stuffer-box conditions may be determined in advance by measuringthe percentage retention of breaking strength of a spliced portion ofthe yarn after submergence in boiling water for one hour. The maximumpermissible loss of splice strength determined by this method, whichwill still afford reliable stufier-box treatment, is a loss of 5%.Splices prepared in accordance with this invention generally lose lessthan 3% of their original strength when tested by this method, andexhibit less than 0.1% failures during stuffer-box operations. It isfound moreover, that the spliced portion of yarn becomes crimped,thereby maintaining the uniformity of the continuous textured yarnstructure.

In the texturing of polyamide yarns by false-twist heat setting methods,as described in U.S. Patents 3,041,814, and 2,987,869, the yarn issubjected to dry heating means which elevate the yarn temperature to therange of 170 C. to 230 C. Under these conditions, ordinary splicesexhibit a high failure rate. It has been found that, as a generalcriterion of satisfactory operation under falsetwist heat settingconditions, the spilced portion should have a breaking strength at least70% as high as an unspliced portion of the same yarn. Splices preparedin accordance with this invention will generally have breaking strengthsin excess of 70% of the yarn tensile strength, frequently havingstrengths above 80% and 90% of the original yarn, and are foundeminently suited for falsetwist heat setting texturing operations.

Although the exact bonding mechanism of the splicing method of thisinvention is not completely understood, it is quite likely that thebonding composition penetrates and spreads practically throughout theyarn bundle, forming the bundle into a tough, flexible, cohesive mass bywetting, tackifying, and slightly dissolving adjacent filaments, withoutcausing filament weakening or complete inter-filament coalescence. Useof nearly saturated solution is important to avoid any extensivedissolving up of the filaments, which would tend to distort and/ orweaken the joint. The cohesive mass is characterized by the absence ofinter-facial areas adhesively attracted by Van der Waals forces ofattraction. It is generally well recognized that adhesive bonds,characterized by Van der Waals forces of surface attraction, exhibitdepreciated bond strengths when intimately contacted by water, since thewater molecules tend to satisfy the attractive surface forces. Cohesivebonds characterized by a continuum of molecules similar or identical tothose of the bonded members intermingled at interatomic distances andmolecularly blended with both bonded members, are unaffected by water orother chemical or physical entities except those which affect thecohesive state of the bonded members. The critically selected bondingcompositions of this invention appear to accomplish the unexpectedfunction of effecting strong cohesive bonding without appreciablyattacking or weakening individual filaments. The resulting joint issmooth and only slightly bulging. Upon passage through the feed rolls ofa crimping apparatus the joint is flattened out, and in this flattenedform it takes a crimp under the same conditions which crimp thefilaments composing the spliced yarn of this invention.

The following specific examples are given to illustrate preferredmethods of carrying out the present invention. It is to be understoodhowever that these examples are not to be considered as limitative ofthe scope of the invention. All parts and percentages are by weightunless otherwise indicated.

EXAMPLE 1 A polycaproamide polymer having a molecular weight of 20,000as determined by viscosity measurement was dissolved in2,2,3,3-tetrafiuoropropanol (B.P. C.) to the point of saturation. Thesaturated solution, at room temperature (24 C.), was found to have aviscosity of 3500 centipoises, and a poylmer content of 12%. The bondingcomposition thus prepared was applied by hand to the ends of a 1200denier 70 filament polycaproamide yarn having been prepared inconventional manner by melt spinning followed by application of alubricating oil finish, and drawing. The two yarn ends containing thebonding composition were then rolled together between the fingers andheld for about two seconds in the ambient air without applying tensionto the freshly formed splice. A non-tacky splice, inch long, was therebyobtained having a breaking strength of 85% of the yarn breakingstrength. After immersion of the spliced portion in boiling water forone hour, followed by re-drying prior to testing, the splice was foundto lose only 1.5% of its original breaking strength.

Yarn containing splices prepared in accordance with this example wassubjected to a continuous stutfer-box crimping operation employingapparatus essentially as described in U.S. Patent 3,037,260, and processconditions essentially as described in U.S. Patent 3,031,734. The yarnwas fed as a 60 end flat ribbon to the crimper at a speed of about 750feet per minute, With a rate of removal from the crimper of about 560feet per minute, an exit gate weight of 1 1b., and a moist yarntemperature of about C. in the crimping zone. The yarn emerging from thestutfer-box had a crimp frequency of about 12 crirnps per inch, and wascrimped in the spliced portions. This yarn was then subjected to acontinuous stretching operation at 175 C. under 750 grams tension; thepurpose of said stretching operation being to impart latent recoveryproperties to the crimped yarn so that textile articles preparedtherefrom would develop improved bulk by exposure of the article toelevated temperatures. The yarn thus textured was convolutely wound onto1b., at profile spools.

The packaged yarn thus prepared was employed in twoply form in themanufacture of a tufted carpet having six tufts per inch and 20 ouncesof fiber per square yard of carpet. The tufting needle had an ovalshaped eye inch high and inch wide, and operated at a rate of 520 tuftsper minute.

In the over-all operation of yarn texturing, stretching and tufting, nosplice failures occurred during the passage of 25-6 splices through theentire operation in the manufacture of a carpet. After dyeing andfinishing, the carpet was of highly uniform quality with none of thesplices being visibly detectable.

By way of contrast, a bonding composition outside the purview of thisinvention was prepared employing the same bonding polymer and solvent asin this example, except that the solution was prepared as an unsaturatedsolution containing only 7% of dissolved polymer and having a viscosityof about 2000 centipoise. When applied in the same manner to the yarn ofthis example, a splice was obtained having only about 55% of the yarnbreaking strength, and was found unsatisfactory in the yarn texturing,stretching and tufting process described above.

By way of further comparison, yarn was spliced employing the bondingcomposition of this invention described in this example, employingconditions identical to those employed above in this example except thatthe length of the spliced portion was made to he /s inch, therebyoutside the scope of this invention. This yarn was then subjected to thetexturing, stretching and tufting operation described above. It wasfound however a failure frequency of approximately 2.5% occurred duringpassage of the spliced portions through the tufting needle.

EXAMPLE 2 TABLE I Polymer Viscosity of Bonding Breaking Strength ofMolecular Weight Composition 1 Splice, Percent 2 1 In centipoises. 2 Aspercent of breaking strength of the yarn.

As the data of Table I indicate, molecular weights of the bondingpolymer below about 15,000 (V. Rel. below about 50) provide spliceshaving unsatisfactory breaking strength. Polymers having formic acidrelative viscosity much above about 350 generally provide, at thedesired concentrations, solution viscosities above 6000 centipoise whichresults in excessive tackiness leading to stringing of the compositionduring application, whereby protruding short filaments are formed.

EXAMPLE 3 A polycaproarnide polymer having a molecular weight of 20,000was dissolved to the point of saturation in a mixture of 45 parts of2,2,2 trifiuoroethanol (B.P. 74 C.) and 55 parts of 2,2,'3,3tetrafluoropropanol (B.P. 110 C.). The bonding composition thus preparedwas applied in amounts less than about /2 gram to the ends of a 1200denier 70 filament polycaproarnide yarn. The two yarn ends containingthe bonding composition were rolled together and held under a stream ofwarm air for about two seconds without applying tension to the freshlyformed splice. A non-tacky splice, inch long, is thereby obtained havinga breaking strength of of the yarn breaking strength. After immersion ofthe spliced portion in boiling water for one hour followed by re-dryingprior to testing, the splice was found to lose only 1.5% of its originalbreaking strength.

In applying the bonding composition of this example in similar fashionto yarns of poly(hexamethylene adipamide), splices are obtained havingbreaking strengths about 82% of yarn strength; said yarns performingsatis factorily in stutfer-box and false-twist heat setting opera tionsto give textured yarns wherein the spliced portion receives an angularor helical crimp analogous to unspliced yarn portions.

EXAMPLE 4 A poly (hexamethylene adipamide) polymer of molecular weight30,000 having been methoxymethylated by treatment with methanol andformaldehyde, was dissolved to the point of saturation in a mixture of60 parts 2,2,3,3 tetrafiuoropropanol and 40 parts methanol. The bondingcomposition thus prepared, having a viscosity of 4500 centipoise, wasapplied to the ends of a 2400 denier filament polycaproarnide yarn. Thetwo yarn ends containing the bonding composition were splayed, placed in/2 inch abutting contact, and held under a stream of cool air for aboutthree seconds without applying tension to the freshly formed splice. Anon-tacky splice was thereby obtain having a breaking strength of 90% ofthe yarn breaking strength.

By way of contrast, a non-polyamide polymer, polymethyl methacrylate,outside the purview of this invention but nevertheless well known as anadhesive ingredient, was employed as the bonding polymer in the practiceof this invention. It was found that, regardless of specific sol-vent,solution concentration, or solution viscosity, splices could not beproduced having breaking strengths higher than 52% of yarn strength. Itwas also found that such splices exhibited adhesive rather than cohesivebonding in view of their excessive strength losses of 10%- 50% inboiling water.

By employing bonding compositions containing less than 17% dissolvedpolymer, and dissolved polymers having molecular weights below about40,000, the bonding compositions of this invention can successfully beemployed without stringing, i.e., the formation of bridging filamentsfrom the dissolved polymer. The stringing effect, characteristic ofprevious compositions of dissolved polymer employed in gluing or coatingoperations is especially undesirable in the course of the splicingprocess of this invention since the presence of protruding filamentarymaterial near the splice leads to snagging during weaving operations,and the stringing effect would create problems in the handling of thebonding composition during the splicing operation.

The bonding compositions of this invention may also be employed toconsolidate untwisted yarns so that they will secure the runabilitycharacteristics of twisted yarns. This may be accomplished by applyingsmall amounts of the bonding composition to a running zero twist yarn atpoints thereon spaced about 1 inch apart. The flexible nature of theinter-filament bonding causes essentially no adverse change in thephysical or aesthetic qualities of the yarn. The bonding compositionsare also useful in the bonding of films, multi-yarn cords, and woven andnonwoven polyamide textile articles; and are generally unaffected by thepresence of lubricating oils, dyes, antistatic agents, water repellants,or other chemical auxiliaries commonly employed with polyamide fibers.The bonding compositions may contain indicating agents such '7 asfluorescent materials to locate the splices or to distinguish one typeof splice from another under ultraviolet light.

As many apparently widely diiferent embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that this invention is not limited to the specificembodiments thereof except as defined in the appended claims.

We claim:

1. A bonding composition comprising a practically saturated solution ofa polyamide having formic acid relative viscosity of at least about 50,in a solvent having a boiling point between 90 C. and 115 C., saidsolution containing between 8% and 17% of said polyamide and having aviscosity between 2500 and 6000 centipoises at room temperature.

2. The bonding composition of claim 1 wherein said solvent comprises anorganic alcohol.

3. The bonding composition of claim 1 wherein said solvent consistsessentially of 2,2,3,3-tetrafiuoropropanol and wherein the polyamide ispoly-e-caproamide having formic acid relative viscosity by ASTM MethodD7 89- 53T of 50350.

4. A process for uniting filaments of multifilament polyamide yarnscomprising applying to said yarns the bonding composition of claim 1,bringing said filaments into intimate contact, and evaporating thesolvent of said bonding composition while said filaments are maintainedin supported contact.

5. The process of claim 4 wherein yarn ends are rolled together prirorto completion of the splicing process, over a length of about fit- /zinch.

References Cited UNITED STATES PATENTS 1/1935 Kellogg 15615=8 4/1964Castle 893 FOREIGN PATENTS 961,763 11/ 1962 Great Britain.

